The breakdown of local and state agencies that tried to respond to Hurricane Katrina has spurred fresh debate about whether disasters of such magnitude ought to be turned over to the U.S. military and other federal authorities to manage at the outset.

National plans developed after the Sept. 11, 2001, terrorist attacks rest on the notion that police, fire and other emergency groups are best positioned to serve as first responders. Federal agencies are supposed to function as backup to state and local ones, and military forces are meant to play a largely supporting role to civilian authorities.

But Katrina showed what can happen when the foundation of this organizational structure is quickly overwhelmed and disintegrates, according to government officials and independent analysts.

"The would-be first responders at the state and local level were themselves victims in very large numbers," Defense Secretary Donald H. Rumsfeld said at a news conference this week. As a result, "we had a situation that was distinctly different than in past events of this type."

Rumsfeld and other senior administration officials this week have resisted entering a public discussion of alternative approaches, insisting that the focus for now stay on cleaning up after Katrina. President Bush and congressional leaders have promised investigations into what went wrong in the response to the hurricane's devastation.

But Rumsfeld said the government would likely address again the question of "lead responsibility" for the Defense Department in disaster response. He noted that the issue was critical not only in responding to a natural catastrophe but also to a terrorist attack, because reliance on local authorities has been the basis of emergency planning in both cases.

Some homeland defense specialists have argued since Katrina struck that national plans must be revised to provide for a bigger and faster federalized effort, particularly in large-scale disasters.

"Only the federal government can mobilize a national response to catastrophic disasters," said James Carafano of the Heritage Foundation, a conservative think tank. "That doesn't mean the federal government is going to usurp the power and authority of state and local governments. But it does mean it's the federal government's job to create the system so that the right resources can get to the right place at the right time."

There is no guarantee that a greater federal role would improve response. Both the Pentagon and the Federal Emergency Management Agency have been widely faulted for not grasping quickly enough the scope of Katrina's damage and not committing sufficient people, supplies and equipment early on.

Historically, practical as well as legal considerations have favored relying on leadership at the grass-roots level.

"The police and fire departments and local emergency-service people are, by definition, the first ones on the scene," said H.K. Park, a former defense official who worked on homeland security issues during the Clinton administration. "And they have the advantage of knowing their communities.

Further, military forces remain constrained from a domestic law enforcement role by the 1878 Posse Comitatus Act. Though the Pentagon has committed more than 8,000 active-duty Army and Marine troops and about 10,000 sailors, it has made it clear that these forces will not perform police functions.

National Guard troops, now numbering more than 46,000, constitute a far larger share of the military presence in the disaster area. They bring two main advantages. First, they possess medical, engineering, communication and logistical skills required in relief work. Second, Guard units, when operating under the command of state governors, are not limited by Posse Comitatus.

Any move to assign greater responsibility to the Pentagon for domestic emergency management is likely to face resistance, particularly since the armed forces are already strained by the conflict in Iraq. Commanders remain sensitive to the notion of U.S. troops becoming an occupying force in their own country.

When Guard forces arrived in New Orleans late last week, Lt. Gen. Russel Honore, who is overseeing military operations in the region, ordered them to point their rifles down to reinforce the message they had come to provide assistance, not occupy the city.

Politically, too, the idea of an enhanced federal role may be a hard sell to some local and state officials if it means diminishing their authority. Louisiana Gov. Kathleen Babineaux Blanco resisted a Bush administration effort last week to exert federal control over all local police and state National Guard units.

Some experts also contend that an attempt to federalize a relief effort could backfire, resulting in less flexibility rather than more.

"You don't want to federalize the Guard," Park warned. "When Guard forces are controlled by the governor, they can engage in law enforcement duties. When federalized, they are subject to Posse Comitatus."

But Carafano and others argue that major disasters require a different approach, with only the federal government able to provide the resources and coordination necessary to manage a catastrophic event.

The problem, Carafano said, is that officials at all levels of government have appeared more inclined to focus on preparing for smaller disasters. As a result, much of the increased funding for emergency-response activities in recent years has gone toward equipment useful to local agencies, such as new fire trucks or protective fencing, that are of little value when overwhelming disasters strike.

"The money should have gone towards the things that enable local and state authorities to plug into a national system -- things like communications, emergency operations centers, training," he said. "All of these would have enabled the mayor of New Orleans to better communicate his needs."